To achieve the desired degree of accuracy in the profile of bent strip it has been found that provision should be made for checking the accuracy of the permanent angular deformation of each bend.
This need arises principally from the tendency of the metal strip to spring back after bending, the extent of spring-back being variable in that it tends to differ from strip to strip and to be dependent on the angle of bend imparted.
In one aspect the invention aims to provide a way of checking or inspecting the permanent angular deformation applied to the strip and in another aspect the invention provides compensation for spring back of the strip. It will be appreciated that these two aspects are linked, in that the inspection principally checks that proper compensation has been made for spring-back, but there may be situations where these two aspects are separately and independently used.
A further aspect of the invention aims to compensate for an error which can arise if the bending tool is movable along a line of action spaced from the point of bending of the strip by an amount greater than the incremental advance of the strip. Under these circumstances, it is desirable to compensate for the fact that one or more previous bends are located between the bending tool and the point of bending of the strip.